Regardless of your scale you will climb a ladder/vine from the same distance as if you were the default scale. This means that at very small scales you will be able to climb while being visibly far from the ladder/vine at that relative scale, and at very large scales you will not be able to climb at all because you will collide with the wall before you can climb.
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Climable blocks only allow climb when your block coordinates align precisely with theirs. In other words, the center of your feet must intersect with the climbable block as if it were a full block. This behavior mirrors that of MC-139063.
When the player is smaller, that would be expected and intentional behavior based off of MC-75542. Though, I can confirm the unusual behavior with the player not being able to ride up blocks while larger/wider than 1 block.